KepCo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the KepCo Observatory clear sky chart from 2005-11-05 to 2017-10-31.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
39%
14928
13%
47268
9%
14899
44%
14899
17%
32403

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
25%
719
7%
2506
5%
716
28%
716
8%
2003
January16th to endNight
29%
768
8%
2688
7%
768
32%
768
10%
2066
February1st to 15thNight
32%
702
8%
2381
7%
700
35%
700
12%
1778
February16th to endNight
38%
632
13%
1945
8%
632
44%
632
17%
1376
March1st to 15thNight
30%
720
9%
2160
6%
720
34%
720
13%
1641
March16th to endNight
30%
768
9%
2005
4%
768
34%
768
15%
1533
April1st to 15thNight
38%
719
11%
1799
5%
719
41%
719
19%
1328
April16th to endNight
38%
530
13%
1610
9%
530
43%
530
18%
1089
May1st to 15thNight
40%
359
15%
1440
15%
359
49%
359
18%
841
May16th to endNight
41%
374
8%
1496
10%
374
47%
374
14%
962
June1st to 15thNight
45%
360
5%
1279
3%
360
46%
360
19%
804
June16th to endNight
44%
360
10%
1147
2%
360
47%
360
23%
693
July1st to 15thNight
58%
340
10%
1351
8%
340
63%
340
34%
603
July16th to endNight
60%
376
20%
1416
24%
354
75%
354
41%
586
August1st to 15thNight
71%
360
24%
1432
31%
358
76%
358
38%
616
August16th to endNight
63%
652
28%
1798
17%
652
70%
652
45%
932
September1st to 15thNight
63%
720
26%
1800
13%
720
67%
720
47%
992
September16th to endNight
58%
716
25%
1944
16%
716
63%
716
32%
1189
October1st to 15thNight
45%
720
16%
2152
14%
720
49%
720
24%
1379
October16th to endNight
39%
768
14%
2475
10%
768
46%
768
17%
1728
November1st to 15thNight
31%
700
10%
2359
8%
700
35%
700
11%
1825
November16th to endNight
26%
759
7%
2559
5%
759
30%
759
8%
2039
December1st to 15thNight
29%
900
8%
2700
5%
900
31%
900
11%
2116
December16th to endNight
23%
906
9%
2826
3%
906
28%
906
8%
2284

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
11%9%36%5%35%5%5%6%36%
48482
Night
12%10%46%5%2445%6%36%
47435
Cloud CoverDay
11%9%46%6%35%5%5%6%35%
48482
Night
12%10%46%5%3445%6%36%
47439
TransparencyDay
47%6%13%19%10%1
48153
Night
47%6%14%20%9%1
47268
SeeingDay
16%21%24%23%11%2
5933
Night
16%19%15%27%17%3
14933

By Month

Percentage Cloud Cover NW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
18%14%6%10%7%34345%21%
1432
16th to endDay
14%16%38%5%33446%28%
1536
February1st to 15thDay
15%16%5%7%5%3445%6%24%
1483
16th to endDay
12%13%48%7%35%5%6%6%26%
1528
March1st to 15thDay
16%15%5%7%5%35%5%5%7%22%
1800
16th to endDay
14%13%6%9%7%45%6%6%7%18%
2218
April1st to 15thDay
10%11%6%11%8%47%5%46%22%
2149
16th to endDay
10%11%48%7%35%5%6%8%28%
2347
May1st to 15thDay
9%9%37%6%46%5%6%7%33%
2511
16th to endDay
13%9%49%7%45%5%6%7%25%
2615
June1st to 15thDay
16%7%37%6%36%5%5%7%29%
2679
16th to endDay
11%8%36%5%36%5%7%6%36%
2802
July1st to 15thDay
44143245%5%7%56%
2523
16th to endDay
321332445%6%61%
2657
August1st to 15thDay
43234235%46%59%
2520
16th to endDay
4313435%45%7%55%
2401
September1st to 15thDay
4313413247%61%
2160
16th to endDay
10%5%25%43445%6%47%
2016
October1st to 15thDay
13%7%35%42445%7%40%
1806
16th to endDay
20%12%35%5%235%35%31%
1747
November1st to 15thDay
20%12%36%5%35%46%6%24%
1497
16th to endDay
19%11%7%7%4246%5%6%24%
1388
December1st to 15thDay
15%11%6%9%6%35%45%6%25%
1260
16th to endDay
19%18%6%8%5%23335%23%
1407
January1st to 15thNight
21%14%6%8%5%33445%21%
2506
16th to endNight
14%18%5%8%5%34346%23%
2688
February1st to 15thNight
16%14%5%7%5%24446%29%
2369
16th to endNight
11%13%46%425%45%8%32%
1945
March1st to 15thNight
14%11%5%8%5%35%5%6%7%25%
2160
16th to endNight
11%12%48%6%35%5%5%6%28%
2001
April1st to 15thNight
10%9%37%6%37%6%6%7%32%
1799
16th to endNight
6%8%46%6%36%5%5%7%38%
1610
May1st to 15thNight
8%5%26%6%4445%7%44%
1439
16th to endNight
12%7%26%6%36%6%6%8%33%
1496
June1st to 15thNight
12%5%24446%5%5%10%37%
1279
16th to endNight
8%5%235%35%5%5%7%46%
1147
July1st to 15thNight
331322345%6%63%
1431
16th to endNight
122223347%69%
1512
August1st to 15thNight
2212223449%64%
1440
16th to endNight
331231436%8%61%
1798
September1st to 15thNight
321221345%7%64%
1800
16th to endNight
8%5%24433448%50%
1944
October1st to 15thNight
13%7%34324446%44%
2152
16th to endNight
18%9%36%43445%5%33%
2475
November1st to 15thNight
22%12%36%5%34446%24%
2359
16th to endNight
20%14%5%9%5%3443423%
2559
December1st to 15thNight
16%13%5%10%6%24445%25%
2700
16th to endNight
19%20%6%7%5%2333423%
2826

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
15%16%6%11%6%45%435%20%
1432
16th to endDay
15%15%5%7%5%3446%5%26%
1536
February1st to 15thDay
14%16%6%6%6%35%45%7%23%
1483
16th to endDay
10%13%47%7%35%6%6%6%26%
1528
March1st to 15thDay
15%14%5%7%7%35%6%5%8%21%
1800
16th to endDay
13%13%6%10%8%36%5%6%5%18%
2218
April1st to 15thDay
10%11%6%11%8%5%6%5%5%7%21%
2149
16th to endDay
9%10%5%8%7%45%5%6%8%28%
2347
May1st to 15thDay
9%8%37%7%46%5%5%6%33%
2511
16th to endDay
13%8%48%8%46%5%6%7%25%
2615
June1st to 15thDay
15%7%37%7%5%5%5%5%6%29%
2679
16th to endDay
10%7%36%6%45%5%5%7%35%
2802
July1st to 15thDay
44233245%5%6%56%
2523
16th to endDay
3313424446%61%
2657
August1st to 15thDay
331442445%6%58%
2520
16th to endDay
4214425%46%7%55%
2401
September1st to 15thDay
4323323347%60%
2160
16th to endDay
9%425%5%3445%6%47%
2016
October1st to 15thDay
13%7%35%42445%8%39%
1806
16th to endDay
18%11%36%5%44446%30%
1747
November1st to 15thDay
18%12%46%5%35%5%5%7%24%
1497
16th to endDay
16%14%6%6%6%45%5%5%5%23%
1388
December1st to 15thDay
14%12%5%9%7%35%5%45%26%
1260
16th to endDay
16%19%6%8%5%3444423%
1407
January1st to 15thNight
19%15%6%10%6%3344420%
2506
16th to endNight
14%17%6%10%6%3445%5%21%
2688
February1st to 15thNight
15%14%6%7%5%24446%28%
2369
16th to endNight
10%12%46%5%25%5%5%7%32%
1945
March1st to 15thNight
13%11%46%7%35%6%6%7%26%
2160
16th to endNight
10%12%48%8%46%46%6%27%
2005
April1st to 15thNight
10%7%47%6%46%6%5%7%32%
1799
16th to endNight
6%7%47%6%47%5%5%8%37%
1610
May1st to 15thNight
8%5%25%6%45%45%6%44%
1439
16th to endNight
10%8%35%5%45%6%6%8%33%
1496
June1st to 15thNight
12%5%25%6%35%5%6%9%37%
1279
16th to endNight
8%5%345%35%5%6%6%44%
1147
July1st to 15thNight
231331345%7%62%
1431
16th to endNight
1112223348%67%
1512
August1st to 15thNight
22322435%8%64%
1440
16th to endNight
221332336%8%62%
1798
September1st to 15thNight
321331345%6%64%
1800
16th to endNight
7%425%5%34448%50%
1944
October1st to 15thNight
12%6%36%4235%46%44%
2152
16th to endNight
17%8%26%5%345%5%5%34%
2475
November1st to 15thNight
20%11%47%6%35%45%5%25%
2359
16th to endNight
19%15%5%8%7%3433423%
2559
December1st to 15thNight
16%14%6%9%6%34445%24%
2700
16th to endNight
18%20%6%8%5%2333422%
2826

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
64%6%12%11%4
1432
16th to endDay
55%7%14%15%41
1536
February1st to 15thDay
59%8%17%12%2
1483
16th to endDay
56%8%13%14%7%
1528
March1st to 15thDay
59%8%14%13%3
1800
16th to endDay
63%8%14%10%3
2218
April1st to 15thDay
61%7%13%13%3
2149
16th to endDay
52%8%14%20%41
2347
May1st to 15thDay
49%6%13%21%8%1
2511
16th to endDay
55%6%15%16%4
2619
June1st to 15thDay
54%5%11%16%8%2
2679
16th to endDay
46%5%12%21%12%
2802
July1st to 15thDay
27%5%10%25%22%8%
2374
16th to endDay
23%5%9%25%28%7%
2490
August1st to 15thDay
25%5%11%30%22%4
2503
16th to endDay
25%7%11%31%20%3
2401
September1st to 15thDay
24%413%30%24%3
2160
16th to endDay
35%8%14%25%13%2
2016
October1st to 15thDay
41%7%15%25%8%
1806
16th to endDay
54%7%13%19%5%
1747
November1st to 15thDay
58%8%14%13%31
1497
16th to endDay
59%8%12%15%4
1388
December1st to 15thDay
58%8%13%15%3
1260
16th to endDay
63%6%12%13%3
1407
January1st to 15thNight
65%5%12%10%4
2506
16th to endNight
61%5%13%12%41
2688
February1st to 15thNight
56%7%16%14%41
2381
16th to endNight
49%7%17%19%6%
1945
March1st to 15thNight
54%8%15%16%3
2160
16th to endNight
54%7%15%17%4
2005
April1st to 15thNight
47%8%15%20%6%
1799
16th to endNight
44%7%15%25%6%
1610
May1st to 15thNight
39%5%14%25%14%1
1440
16th to endNight
44%7%19%21%6%
1496
June1st to 15thNight
41%6%14%25%10%1
1279
16th to endNight
35%6%15%25%15%1
1147
July1st to 15thNight
21%412%27%24%9%
1351
16th to endNight
16%411%28%29%9%
1416
August1st to 15thNight
18%5%12%32%25%5%
1432
16th to endNight
19%5%13%33%24%3
1798
September1st to 15thNight
19%5%12%29%27%4
1800
16th to endNight
33%6%12%29%15%3
1944
October1st to 15thNight
39%6%16%24%12%
2152
16th to endNight
49%6%13%24%5%
2475
November1st to 15thNight
59%8%12%13%41
2359
16th to endNight
64%5%10%12%5%
2559
December1st to 15thNight
60%6%13%14%3
2700
16th to endNight
66%6%9%13%4
2826

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
16%6%11%33%23%8%
60
16th to endDay
39%6%17%23%9%4
64
February1st to 15thDay
23%19%25%23%6%
143
16th to endDay
18%20%21%27%9%1
229
March1st to 15thDay
31%31%25%10%1
270
16th to endDay
24%35%20%15%4
288
April1st to 15thDay
21%27%26%15%7%1
269
16th to endDay
17%33%23%15%6%3
270
May1st to 15thDay
18%29%25%20%6%
288
16th to endDay
18%19%23%20%14%5%
330
June1st to 15thDay
13%20%23%24%15%2
474
16th to endDay
11%23%23%24%13%2
597
July1st to 15thDay
7%18%26%33%11%2
308
16th to endDay
320%32%27%12%3
327
August1st to 15thDay
8%12%23%34%14%6%
315
16th to endDay
6%18%26%31%10%5%
332
September1st to 15thDay
7%21%24%26%15%4
315
16th to endDay
14%16%26%25%13%3
315
October1st to 15thDay
20%19%27%21%8%1
315
16th to endDay
32%9%21%22%13%1
165
November1st to 15thDay
30%12%25%26%5%
75
16th to endDay
25%13%23%10%18%10%
60
December1st to 15thDay
26%6%25%25%13%3
60
16th to endDay
26%7%25%23%12%4
64
January1st to 15thNight
22%23%14%25%11%2
720
16th to endNight
19%20%16%27%14%1
768
February1st to 15thNight
19%21%14%25%15%2
704
16th to endNight
16%20%16%27%16%3
632
March1st to 15thNight
19%24%18%24%11%1
720
16th to endNight
16%24%20%24%11%1
768
April1st to 15thNight
11%22%17%26%17%4
719
16th to endNight
9%24%19%29%14%3
530
May1st to 15thNight
10%24%16%29%16%2
360
16th to endNight
14%20%13%25%20%5%
375
June1st to 15thNight
10%21%15%29%20%2
360
16th to endNight
11%20%17%28%20%2
360
July1st to 15thNight
5%17%14%26%31%4
340
16th to endNight
221%11%30%30%4
376
August1st to 15thNight
212%9%26%40%8%
360
16th to endNight
413%14%31%29%5%
652
September1st to 15thNight
413%14%27%27%11%
720
16th to endNight
11%11%10%33%26%6%
716
October1st to 15thNight
18%13%16%27%22%2
720
16th to endNight
23%11%16%29%16%3
768
November1st to 15thNight
23%22%15%29%8%1
700
16th to endNight
25%24%12%21%12%3
759
December1st to 15thNight
21%23%15%30%8%1
900
16th to endNight
26%22%18%26%6%
906
Page generated at 2017-11-01 14:23:41. Version ac04

Copyright 2017 A. Danko


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